Nils suggested in the open Sunday thread that I talk about the advantages and disadvantages of consoles vs. PC when it comes to playing MMORPGs. Now this is a case where platform choice is usually made extremely quickly, given the fact that there are only a small number of console MMORPGs, and lots of them on the PC. But I just signed up for the Final Fantasy XIV beta (after a guild mate told me that you get a code for the beta when you register you FF13 game), and when asked whether I wanted to test and ultimately play FF14 on the console or on the PC, I chose the console.
Now that choice was made from my experience with FF11, which also existed on either console or PC, and which I played on the PC. It turned out that the UI and controls were designed with the console in mind, and were not all that user-friendly for a keyboard and mouse. So I ended up playing FF11 on the PC using a gamepad, which made controls much smoother. But once you go for console-like controls, you might as well play the whole game on the console.
The main problem with playing a MMORPG on a console is chat, if you don't have a keyboard installed. Typing with a gamepad is annoying. But then FF11 had this wonderful chat system where you could string words together by choosing them from a menu. That is obviously more limited than free form chat, but a surprising amount of chat in a MMORPG is rather predictable, like "looking for group" or "WTS this item". What made the chat system of FF11 so great was that it was automatically translated to whatever language the guy on the other end was having his client in. That made it possible to group with Japanese players even if they didn't speak English.
For the rest of the controls, it all depends on game design. If you have a game design requiring 50 different buttons, a gamepad is not always optimal. But if you design the game around the controls, it is perfectly possible to create an interesting combat system which is controlled very well with a gamepad. And I always liked having one thumbstick to move my character and a second thumbstick to move the camera, a control scheme which I consider superior to mouse/keyboard controls of characters through 3D worlds.
So in summary, I think that the current obstacles to playing MMORPGs on a console can be overcome, if the game is designed right. Just don't expect a game designed for the PC to be easily ported to a console.